Industrial applications of ceramics have become increasingly important over the last fifty years. Monolithic ceramics and cermets, however, exhibit low impact resistance and low fracture toughness. Ceramic Matrix Composites (CMCs) exhibit some useful thermal and mechanical properties and hold the promise of being very good materials for use in high temperature environments and/or in heat sink applications. CMCs generally comprise one or more ceramic materials disposed on or within another material, such as, for example, a ceramic material disposed within a structure comprised of a fibrous material. Fibrous materials, such as carbon fiber, may be formed into fibrous bodies suitable for this purpose.
Carbon fiber bodies are typically formed from carbon fiber body precursors. For example, preoxidized polyacrylonitrile (PAN) is commonly used as a carbon fiber body precursor. Carbon fiber body precursors may be manipulated and fabricated in a manner similar to a textile (e.g., weaving, knitting, etc) to form desired structures. To transform the carbon fiber body precursor into a carbon fiber body, various methods and techniques may be used. For example, during transformation of PAN materials, the PAN fiber may be carbonized and then processed to eliminate impurities (often metallic) that may be found in the PAN fiber. Sodium is a common metal found in PAN fibers that may be removed during processing into a carbon fiber body. Other carbon fiber body precursors may contain impurities comprising magnesium, calcium, iron, nickel, or chromium, in addition to sodium.
Transformation of carbon fiber body precursors, such as PAN fibers, often occurs in a two stage process. The first stage may be a carbonization stage. A carbonization stage is typically performed at temperatures of less than 1100° C., and most typically between about 800° C. and 950° C. The second stage may be a high temperature stage, typically using temperatures over 1400° C.
However, while the second stage causes the PAN fibers to release residual impurities (also referred to herein as residual materials) in a gaseous state, the subsequent management of the residual impurities is often problematic. For example, sodium is a highly reactive metal. As a gaseous stream exits the process vessel, sodium contained therein may react with other materials in the gaseous stream and/or the pipes and other devices that contain the gaseous stream. Such reactions weaken the integrity of the components that come into contact with the gaseous stream, thus reducing useful product life and presenting a risk of dangerous malfunction. Further, as sodium leaves the gaseous state, it may cause damage to other processing hardware, which may be costly to replace.
Although conventional methods of managing sodium include injecting water or carbon dioxide into the gaseous stream immediately after the gaseous stream exits a furnace at a point where all sodium contained in the gaseous stream is in a gaseous state, routine cleaning and incomplete neutralization issues persist. Accordingly, there is a need for improved management of residual materials, such as sodium, in such an industrial process. In this regard, it is desirable to construct a system having improved management and removal of residual impurities wherein a gaseous stream containing sodium is directed through a heated zone and a cooled zone to better facilitate the removal of residual impurities. Additionally, it is desirable to perform one or more neutralization steps to better manage residual impurities.